I know what you mean...
You say 'I know what you mean' like it's the most profound thing ever, even though you're just trying to get out of talking.
They ask for advice. You say, 'I know what you mean,' and then walk away.
They tell you about their problems. You say, 'I know what you mean,' and then pretend you're busy.
They try to explain their feelings. You say, 'I know what you mean,' and then go play video games.